1. Field of the Invention
The present invention relates to an engine cooling system for an off-road vehicle, including a thermostat placed in a coolant circulating passage extending between the cylinder block, provided with water jackets, of an engine and a radiator.
2. Description of the Related Art
A prior art engine cooling system for an off-road vehicle has a thermostat case for holding a thermostat, held by a bracket on a body frame of the vehicle or cylinder unit of an engine included in the vehicle as mentioned in JP-A 2002-220076 or formed integrally with a component member of the engine, such as a cylinder head or a cylinder head cover.
The use of the bracket for holding the thermostat case on the body frame or on the cylinder unit increases number of parts for forming a piping system, the weight of the piping system of the cooling system and assembling work. Particularly, when the thermostat case is held on the body frame the thermostat case is spaced from the cylinders. Therefore, the thermostat is unable to respond quickly to the change of the temperature of the coolant and the operation of the thermostat is delayed. For example, the thermostat remains closed and the coolant flows slowly through water jackets of the engine after the start of the engine until the temperature of the coolant rises to a predetermined level. When the thermostat is disposed far from the engine, the thermostat senses the rise of the temperature of the coolant to the predetermined level some time after the temperature of the coolant has risen to the predetermined level, the opening operation of the thermostat is delayed. Thus, the thermostat is unable to respond quickly to the rise of the temperature of the coolant.
When the off-road vehicle is equipped with a V-type engine, the coolant flowing through water jackets in each of all the cylinder units must be collected at a single collecting part and needs to be carried from the single collecting part to the thermostat. If the thermostat case is disposed far from the V-type engine, number of parts for forming the piping system of the cooling system, the weight of the piping system and assembling work increase